1. Field of the Invention
The present invention relates to a hybrid differential gear device, differential case therefor and an assembling method of the differential case, and more particularly relates to a hybrid differential gear device, differential case therefor and an assembling method of the differential case having a pinion shaft rotatably supported a pinion gear engaging with a side gear.
2. Description of the Related Art
It is well known for a prior hybrid differential gear device having two differential gear mechanism installed in parallel to a direction of a tire shaft axis as disclosed in a published patent document; Tokkai 2003-130178, especially in FIG. 4 thereof. It is also well known for a prior hybrid differential gear device distributing torque input from a ring gear, mounted on a peripheral surface of a differential case, into two driving shafts as disclosed in a published patent document; Tokkai 2004-347012.
The prior differential gear device disclosed in the Tokkai 2003-130178 provides a first differential gear mechanism as a center differential gear mechanism of a planetary gear type differential gear mechanism, a second differential gear mechanism as a front differential gear mechanism of a bevel gear type differential gear mechanism, and a differential case installing the first and the second differential gear mechanisms.
The first differential gear mechanism has a planetary gear as a first input element, a sun gear as a first output element engaging with the planetary gear, and an internal gear as a second output element engaging with the planetary gear on an axis same to an axis of the sun gear. The second differential gear mechanism has a pinion shaft supported by the internal gear, a pair of pinion gears as a second input element supported rotatably on the pinion gears, and a pair of side gears as a third output element and a forth output element engaging with the one pair of pinion gears. The differential case is formed by a case body having a first ring gear mounting flange, and a cap having a second ring gear mounting flange.
The planetary gear rotates by receiving a rotational force of the differential case to transmit this rotational force to the sun gear and the internal gear. The sun gear rotates by receiving the rotational force of the planetary gear to transmit this rotational force to a rear tire shaft as an output shaft. The internal gear rotates by receiving the rotational force of the planetary gear to transmit the rotational force to the pinion gear shaft.
The pinion gear shaft rotates by receiving the rotational force of the differential case to transmit this rotational force to the one pair of pinion gears. The one pair of pinion gears rotates by themselves or in planetary rotation by receiving the rotational force of the pinion gear shaft or the internal gear to transmit this rotational force to the one pair of side gears. The one pair of side gears rotate by receiving the rotational force of the one pair of pinion gears to transmit this rotational force to a right and a left front tire wheel shafts.
The differential case rotates by receiving torque from the ring gear in an engine side of a vehicle to transmit this rotational force to the planetary gear.
In this construction of the prior hybrid differential gear device, the torque from the engine is input into the differential case to rotate the differential case around a rotational axis. Upon the rotation of the differential case, the rotational force is transmitted to the planetary gear and to the internal gear and the sun gear through the planetary gear. Thereby, the internal gear and the sun gear are rotated to transmit the rotational force to the one pair of pinion gears through the pinion gear. Therefore, the one pair of pinion gear is rotated by themselves or in planetary rotation to transmit this rotational force to the one pair of side gears.
In this state, since the output shaft is engaged with the sun gear and the right and left front tire wheel shafts are engaged with the one pair of side gears, the torque from the engine is transmitted to the output gear through the differential case and the planetary gear and the internal gear of the first differential gear mechanism and then transmitted to the right and left front tire wheel shafts through the differential case, the planetary gear and the internal gear of the first differential gear mechanism and the pinion gear and the side gears of the second differential gear mechanism.
In this prior hybrid differential gear device, by the way, a position of the pinion shaft in a direction of an axis of the tire wheel shaft, that is a direction of the rotational axis, depends on a position of the internal gear in the rotational axis direction because the pinion gear shaft is supported by the internal gear. Therefore, where the internal gear the planetary gear and the sun gear are consisted of a helical gear, the rotational force of the differential case is transmitted to the planetary gear to generate thrust force in the planetary gear and the sun gear so that the internal gear and the sun gear are moved to approach each other along the rotational axis of the differential case, thereby to move the pinion gear shaft to the sun gear side with the internal gear. In this instance, the side gear in the sun gear side receives load from the pinion gear shaft through the pinion gear and also receives the thrust force generated in the sun gear so that it intends to destroy a stable performance of the engagement between the pinion gear and the side gear and to reduce durability. Therefore, a wall is mounted on the differential case between the sun gear and the side gear in order to receive the thrust force generated on the sun gear to prevent the thrust force from being received by the side gear in the sun gear side to make the stable performance and to prevent the durability from reducing.
However, the prior hybrid differential gear device is constructed with the wall between the sun gear and the side gear, thereby to make a size of the differential case to the rotational axis direction large and it creates the problem for the whole device to become large and heavy.
In another view point of an assembling method of the prior hybrid differential gear device disclosed in the Tokkai 2003-130178 or in the Tokkai 2004-347012, a mounting method of the ring gear to the differential case is performed by the step of inserting a ring gear mounting bolt into a bolt inserted hole mounted on a second ring gear mounting flange and into the ring gear, then screwing the ring gear mounting bolt into a bolt mounted hole installed in the first ring gear mounting flange of the case body.
In the prior hybrid differential gear device disclosed in the Tokkai 2004-347012, the planetary gear, the internal gear and the sun gear are constructed with the helical gear in order to create differential limiting force by pressing the planetary gear to the rotational axis direction in transmitting the torque. This pressing force acts to spread the differential case to a direction of the output shaft. And also in the prior hybrid differential gear device disclosed in the Tokkai 2003-130178, an another pressing force by the bevel gear type differential mechanism acts on the differential case to be spread to the direction of the output shaft in addition to the pressing force by the planetary gear type differential gear mechanism in same condition to the Tokkai 2004-347012. However, the differential case is constructed with two divided parts to be combined by a bolt at a mounting portion of the ring gear so that it is difficult to establish sufficient intensity of the flange and a combining force by the bolt. Therefore, in order to combine the two divided parts by bolt, it is needed that a width of the flange is large or a number of bolts is increased to establish the sufficient strength and combined force at the combined portion. As a result of that, it needs more weight and assembling time.